This invention relates to a gas flow sensor used with a chemical oxygen generation device to signal a rate of generation of oxygen less than a predetermined magnitude.
Chemical oxygen generation elements formed principally of a chemical compound capable of generating oxygen by a chemical reaction or pyrolysis are suitable for use in a portable, small-sized oxygen generation device because there is no necessity of employing heavy, pressure-resisting vessels such as are necessary for holding compressed oxygen. One of the most typical examples of such an oxygen generation element is the chlorate system including principally alkali metal chlorate, for example, sodium chlorate having added thereto an exothermic agent such as a powder of reduced iron and a chlorine absorbent such as barium peroxide, the components being shaped into candles by filling canisters with a mixture of the components. Those oxygen generation elements are called "chlorate candles" and when one end thereof is strongly heated by a detonator, an electric heater or the like, the oxygen generation elements generate heat while decomposing and emitting to oxygen. Thereafter the elements touch off chain reactions by means of the decomposition heat generated thereby to continue to emit the oxygen.
There is a problem in the use of oxygen generation devices employing a chemical oxygen generation element as above described in that it is difficult to estimate how much longer the element will continue to generate oxygen after initiation. The ability to generate oxygen remaining after the candle has been burning for a while might be approximated to some extent on the basis of both a nominal rate of generation of oxygen of the particular oxygen generation element and the lapse of time after the initiation of generation of oxygen. However it is difficult always to know the exact time of burning unless a timer is attached to the oxygen generation element. Also, even if this were possible, the rate of generation of oxygen is somewhat variable among different oxygen generation elements. Finally, an oxygen generation element failure before the completion of decomposition is always a possibility, even if remote. Therefore, a means to continuously monitor the status of the oxygen generation (the cessation of the oxygen generation or when that cessation is near at hand) is desirable. This is because the time at which the particular oxygen generation element will stop generating oxygen can not be accurately anticipated.
The monitoring of the generation of oxygen can be based on sensing by the user with simple devices. However, in oxygen generation devices including a plurality of oxygen generation elements to be sequentially decomposed by heat to continuously generate oxygen for artificial respiration devices used in case of emergency, it is unreasonable to expect monitoring of such a device by the user himself or herself. Under these circumstances, it is desirable to provide means for rapidly sensing the cessation of generation of oxygen or the approaching cessation thereof with a high accuracy.
Accordingly it is an object of the present invention to solve the problems as above described.